Optimal design of the transmission-way of mechanical stress throughthe interface between a joint prosthesis and bone tissue together with the criterion formulation for the assessment of the fixation method

超高分子量聚乙烯（UHMWPE）在关节假体强度设计中应明确失效准则。在本研究中，我们在与全膝关节假体相似的条件下对UHMWPE钢板进行了压缩试验并进行了有限元分析，并讨论了失效标准。由常规或交联超高分子量聚乙烯制成的平板被模塑为试件。厚度从2毫米到8毫米不等。压缩试验采用装载机，在37℃的盐水浴池中进行。压头采用直径50毫米的金属球体。载荷为6kn，十字头速度为每分钟2mm。试验结束后，以压入面积与最大负荷之比计算流量压力。板的变形通过边缘的位移来估计。此外，在虚拟模型上使用与实验相同的条件进行了有限元分析。常规超高分子量聚乙烯的平均流动压力为32.8 MPa， SD为2.3 MPa；交联超高分子量聚乙烯的平均流动压力为37.3 MPa， SD为0.9 MPa。超高分子量聚乙烯板的位移随板厚的减小而增大。有限元分析估计的位移与实验结果相似。此外，有限元模型UHMWPE板的剪切应变随位移的增加而增加。研究结果表明，超高分子量聚乙烯（UHMWPE）关节假体的失效标准不仅包括应力，还包括应变。植体加压固定后，骨组织中的应力必须保持不变。残余应力必须引起植入物周围的生物反应。由于残余应力是静止的，与生理力学条件不同，这种效应尚未得到充分的讨论。在本研究中，我们开发了一种使用具有超弹性的针在大鼠股骨内配置固定应力场的方法。结果显示，在骨髓内钉固定负荷6周后，股骨边缘出现骨肥大。少

Failure criteria of ultra-high molecular weight polyethylene (UHMWPE) should be clarified for the strength design of joint prostheses. In the present study, we performed compression tests of UHMWPE plates together with finite element (FE) analysis under conditions similar to those within a total knee prosthesis and discuss the failure criteria.Flat plates made of conventional or cross linked UHMWPE were molded as test pieces. Those thicknesses were ranging from 2 mm to 8 mm. The compression test using a loading machine was performed in a bath filled with saline solution at 37 degrees centigrade. A metallic sphere 50 mm in diameter was used for the indenter. The load was applied to 6 kN under a crosshead speed of 2 mm per minute. Flow pressure was calculated after the test as a ratio of the impressio area and the maximum load. Deformation of the plate was estimated by displacement at the edge. Additionally, the FE analysis was performed on a virtual model using the same conditions as in … More the experiments.The values of the flow pressure were measured as a mean of 32.8 MPa, SD 2.3 MPa for conventional UHMWPE, and as a mean of 37.3 MPa, SD 0.9 MPa for cross-linked UHMWPE. The displacement of the UHMWPE plate increased with decreasing thickness of the plate. The displacement estimated by FE analysis was similar to that of theexperimental findings. Furthermore, shear strain in the UHMWPE plate of FE model increased with the displacement. It was concluded that the failure criteria of joint prostheses must be presented by not only the stress but also the strain in a UHMWPE insert.Stress in bone tissue must be remained after the press-fit-fixation of a implant. The residual stress must bring on the biological response around the implant. The effect has not been sufficiently discussed, yet, because the residual stress is stationary and unlike the physiological mechanical conditions.In the present study, we developed a method to configure stationary stress field in a rat femur using a pin with the hyper elasticity. As the results, it was observed that bone hypertrophy emerged at the fringe of the femur under six weeks stationary load from the pin inside bone marrow. Less